Exhaust gas heat recovery system

ABSTRACT

Envisaged is an exhaust gas heat recovery system comprising a heat pump, a mixer and a flow regulating means. The heat pump is configured to pump heat from a refrigerant. The heat pump has an inlet and an outlet wherein the exhaust gas stream leaving the outlet is split into two streams: a stream rejected to atmosphere and a recirculating exhaust stream re-circulated back to the heat pump. The mixer is provided at the inlet of the heat pump to mix an inlet exhaust stream with the recirculating exhaust gas stream to get a resultant exhaust stream at an intermediate temperature of the two streams. The flow regulating means is adapted to compress the recirculating exhaust stream.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/881,150, filed Jan. 26, 2018, which is a continuation ofInternational Patent Application No. PCT/IB2016/054022, filed or Jul. 5,2016; the entire disclosures of which are hereby incorporated herein intheir entirety.

FIELD

The present invention generally relates to the field of thermodynamics.

Particularly, the present invention relates to self-cleaning metalhydride heat recovery systems such as metal hydride heat pumps.

BACKGROUND

In a typical engine, 35-40% of the fuel energy is released in the formof exhaust gas heat, which can be as high as 500-600° C. for high speedengines. Exhaust driven sorption heat pumps, like absorption heat pumps,metal hydride heat pumps, and adsorption heat pumps, are being in use torecover heat from exhaust gases and convert the same to provide coolingand/or heating inside the vehicle. The outlet temperature of the exhaustgas after heat recovery in the heat pump can be up to 200° C.

A major issue in relation to typical metal hydride heat pumps is thatideally, a sorption bed temperature of such a pump is in the range ofabout 80° C. to 200° C., while an exhaust temperature requirement is ofabout 100° C. to 250° C. depending on beat rejection temperature andcooling temperature requirements. Further, exhaust gases have dust andsoot, which settle on a heat exchanging surface of a heat exchanger of ametal hydride heat pump. Also, when exhaust gases are cooled totemperatures below 250° C., condensation of acid exhaust gasconstituents as well as deposits of exhaust gas constituents occur,which leads to the clogging of the heal exchanger, thereby hampering itsefficiency. The exhaust gas condensate is corrosive and is produced whenthe temperature drops below the dew point. This corrosive exhaust gascondensate will eventually produce corrosive effects in components ofthe metal hydride heat pump such as fins and tube surfaces.

FIG. 1 illustrates a conventional sorption heat pump 100 for exhaust gasheat recovery. A desorber 3 of the sorption heat pump 100 receivesexternal heat input for desorption of a refrigerant material from asorbent media. In a typical metal hydride heat pump, hydrogen is used asthe refrigerant material while a metal hydride alloy acts as the sorbentmedia. The desorber 3 receives external heat input in the form of a hightemperature exhaust gas. An exhaust, gas inlet 1 to the desorber 3provides exhaust gases from an engine of temperatures up to 500-600° C.This exhaust gas is cooled by the sorbent media, i.e., the metal hydridealloy. A desorber outlet stream 4 of the exhaust gas that is released tothe atmosphere via for example a chimney is typically at 100-200° C. Theexhaust gas stream passes through a plurality of passes 5 and a numberof flow reversals 6 to achieve a better heat transfer rate. In themethod as described above, exhaust gases at a high temperature are useddirectly as input. The arrangement has certain limitations which are asfollows.

The direct use of exhaust gases having temperature as high as 500-600°C. can lead to overheating of heat transfer surfaces like tube and tinsof the heat exchanger, whereas typical required temperatures for theoperation of the heat pump is only 100-200° C. Further, as the metalhydride heat pump operation is cyclic in nature and requires alternateheating and cooling of the heat exchanger and sorption materials in eachcycle, overheating of the heat exchanging surfaces results in a higherthermal inertia of metal hydride and the heat pump. Higher thermalinertia is highly undesirable for the performance of the metal hydrideheat pump and the adsorption heat pump. The increased thermal inertiareduces cooling capacity and COP (co-efficient, of performance) of thewhole of the system.

Further, direct use of the exhaust gases results in higher temperaturedifference of up to 400° C. across the heat exchanger. This results inhigher variation in the volumetric flow, hence large variation ofvelocity of the exhaust gas in the beat exchanger. This reduces heattransfer rate, thus resulting in higher size of the heat exchanger.

Furthermore, direct use of the exhaust gases requires several passes tobe provided to maintain velocity in the heat exchanger. The exhaust flowquantity is small compared to treat content and a size of the heatexchanger. More the number of passes and flow reversals, higher thepressure drop through the heat exchanger. Further, small quantity ofexhaust gases in the heat exchanger having a relatively large size leadsto a non-uniform distribution of the exhaust gases over the heatexchanger, which results in reduced performance of tire heat exchangerand the whole of the system.

In addition, there is a higher differential expansion in the heatexchanger due to the use of high temperature direct exhaust gases. Thismay sometimes result in failure of tubes, reducing the reliability ofthe heat exchanger and the system itself. Also, there is possibility ofthermal creep failure as the whole operation is cyclic and alternatesbetween ambient to exhaust temperature. In conventional systems, acyclic temperature difference will be typically up to 500° C. and due toa reduced cyclic temperature difference, thermal creep will be higher.This will result in reduced life and lower number of cycles of operationof the system.

Moreover, to construct a heat exchanger that uses high temperatureexhaust gases, the material needs to be suitably chosen. This may makethe heat exchanger expensive.

Published US patent document US20140047853 discloses a motor vehicleclimate control system that implements two heat transfer fluid (HTF)circuits—a cold HTF and a hot HTF circuit. Exhaust gas heat recovery isused in the hot HTF circuit for recovering heat and transferring it toan adsorption driven heat pump system. It is to be noted here thatimplementation of a circuit like this requires additional heatexchangers for a) transferring exhaust gas heat to a heat transferfluid; and b) rejecting heat of adsorption via the heat transfer fluidto the atmosphere. Use of such circuit for heat transfer also requiresadditional pumps for circulation of fluid and multiple valves for achangeover of the cycle. T his makes the whole system more complex,consuming more auxiliary power and also less reliable due to a number ofmoving putts. The system will also be bulky and expensive.

Another US published patent document US 20050274493 A1 discloses a metalhydride-based vehicular exhaust cooler that works at about 1000° F.(appx. 600° C.) exhaust heat temperature. This system uses eight valvesand a prolonged operation at a high temperature, which leads to thermalinertia and reduced performance. It does not address issues relating tooverheating of heat transfer surfaces, higher thermal inertia, andissues related to performance and efficiency.

Thus, there is a need to minimize the dust and soot and increase theoverall efficiency as well as better heat transfer rate of healregeneration module.

Objects

Some of the objects of the present invention, which at least oneembodiment satisfies, are described herein below:

It is an object of the present disclosure to ameliorate one or moreproblems of the prior art or to at least provide a useful alternative.

It is an object of the present invention is to provide an exhaust gasheat recovery system which is efficient in terms of cooling capacity andcoefficient of performance as compared to conventional systems.

It is an object of the present invention to provide an exhaust gas heatrecovery system having self-cleaning metal hydride regeneration.

It is an object of the present, invention to provide an exhaust gas heatrecovery system having an improved heat transfer rate.

It is an object of the present invention to provide an exhaust gas heatrecovery system that is compact and manageable.

It is an object of the present invention to provide an exhaust gas heatrecovery system that is reliable, less expensive and high in efficiency.

It is an object of the present invention to increase the number ofcycles of operation of the system and thus the life of the system.

Other objects and advantages of the system of the present disclosurewill be more apparent from the following description when read inconjunction with the accompanying figures, which are not intended tolimit the scope of the present disclosure.

SUMMARY

Described herein is an exhaust gas heat recovery system comprising aheat pump, a mixer, and a flow regulating means. The heat pump isconfigured to pump heat from a refrigerant. The heat pump has an inletand an outlet wherein the exhaust gas stream leaving the outlet is splitinto two streams: a stream rejected to atmosphere and a recirculatingexhaust stream re-circulated back to the heat pump. The mixer isprovided at the inlet of the heat pump to mix an inlet exhaust streamwith the recirculating exhaust gas stream to get a resultant exhauststream at an intermediate temperature of the two streams. The flowregulating means is adapted to compress the recirculating exhauststream.

In an embodiment, tire heat pump is a sorption heat pump having adesorber for desorbing a refrigerant material by taking heat from a heatsource.

In an embodiment, the resultant exhaust stream has the same heat contentas that of the inlet exhaust stream but an increased flow rate and alower temperature as compared to the inlet exhaust stream. Preferably,the direction of flow of ambient air is opposite to the direction of/lowof exhaust gases through the heat pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure will now be explained inrelation to the non-limiting accompanying drawings, in which:

FIG. 1 illustrates a block diagram of conventional sorption heat pumpfor exhaust gas heat recovery:

FIG. 2 illustrates a block diagram of an exhaust gas recirculationsystem, in accordance with an embodiment of the present disclosure:

FIG. 3 illustrates an arrangement for heat recovery from exhaust gasrecirculation system in a rotating type metal hydride heat pump, inaccordance with an embodiment of the present disclosure;

FIG. 4 illustrates an arrangement for heat recovery from exhaust gasrecirculation system in a damper type metal hydride heat pump, inaccordance with an embodiment of the present disclosure;

FIG. 5 illustrates a graph showing a desorber input heat duty fromexhaust gases over time for a conventional exhaust system versus that ofa heat pump having, the system as described herein;

FIGS. 6A and 6B illustrate a self-cleaning arrangement in a rotatingreactor type metal hydride heat pump, in accordance with an aspect ofthe present disclosure; and

FIGS. 7A and 7B illustrate a self-cleaning arrangement in a damper typemetal hydride heat pump, in accordance with an aspect of the presentdisclosure.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

An exhaust gas heat recovery system (hereinafter referred to as the‘system’) of the present disclosure will now be described with referenceto the accompanying drawings which do not limit the scope and ambit ofthe present disclosure. The description provided is purely by way ofexample and illustration.

The embodiments herein and the various features and advantageous detailsthereof are explained with reference to the non-limiting embodiments inthe following description. Descriptions of well-known components andprocessing techniques are omitted so as to not unnecessarily obscure theembodiments herein. The examples used herein are intended merely tofacilitate an understanding of ways in which the embodiments herein maybe practiced and to further enable those of skill in the art to practicethe embodiments herein. Accordingly, the examples should not beconstrued as limiting the scope of the embodiments herein.

The description hereinafter, of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such spec ilk embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of preferred embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of theembodiments as described herein.

The system and/or method as described herein relate to exhaust gas heatrecovery using recirculation of exhaust gases. The system is athermodynamic-mechanical arrangement designed to be used in variousapplications including waste heat based cooling, heating, refrigerationand air-conditioning.

The system and/or method for exhaust gas heat recovery as proposedherein are based on remixing of exhaust gases. In accordance with anaspect of the present disclosure, inlet high temperature exhaust gasesas received from an engine are diluted using an exhaust outlet. Apartial flow from the exhaust outlet is re-circulated using a fan and ismixed with the inlet high temperature exhaust gases, which results inexhaust gases having same heat content but a reduced temperature and ahigher flow.

Recirculation flow can be decided as per temperature requirement of thesystem, preferably in a range of 0.1-10 times of exhaust flow.Recirculation rate will be lower if an inlet exhaust temperature islower or the system requires a relatively higher temperature source.Likewise, recirculation rate will be higher if the inlet exhausttemperature is higher or the system requires a relatively lowertemperature source.

FIG. 2 illustrates a block diagram of an exhaust gas recirculationsystem 200, in accordance with an embodiment of the present disclosure.The system 200 consists of a sorption heat pump 18 having a desorber 19for desorbing a refrigerant material by taking heat from a heat source,such as an engine. A mixer 12 is provided to mix an inlet exhaust stream11 with a recirculating exhaust gas stream 16 to get a resultant exhauststream 13 at an intermediate temperature of the two. In an embodiment,the mixer includes a first inlet for receiving the recirculating exhauststream, a second inlet for receiving the inlet exhaust stream and anoutlet adapted to deliver the resultant exhaust stream.

The resultant exhaust stream 13 has the same heat content as that of theinlet exhaust stream 11 but an increased flow rate and a lowertemperature as compared to the inlet exhaust stream 11. The resultantexhaust stream 13 is an inlet condition of exhaust gas to the desorber19 while a desorber outlet stream 14 is an exhaust gas condition at adesorber outlet. The desorber outlet stream 14 is split into twostreams: stream 15 and recirculating exhaust stream 16 (also referred as“recirculating exhaust gas stream 16”). While the stream 15 is rejectedto the atmosphere from an exhaust outlet 20, for example, a chimney, theremaining. i.e., the recirculating exhaust stream 16 is re-circulatedhack to the mixer 12. For the purpose, a flow regulating means isprovided, which includes, for example, a recirculation fan 17. The flowregulating means is also adapted to compress the recirculating exhauststream 16 to a mixer pressure.

As can easily be appreciated from the figure, a mass flow of theresultant exhaust stream 13 is equivalent to the sum of mass flows ofthe inlet exhaust stream 11 and the recirculating exhaust stream 16.Also, the mass flow of the resultant exhaust stream 13 is equivalent tothe desorber outlet stream 14, which is in turn equivalent to a sum ofmass flows of the streams 15 and recirculating exhaust stream 16.

Due to the mixing of recirculating exhaust gas with the inlet exhaustgas in a mixer, a temperature of resultant exhaust gas gets reduced.Also, the resultant exhaust flow after the mixing gets higher ascompared to the inlet exhaust gas stream 11 as received from the engine.

For an inlet exhaust stream 11 (also referred as “inlet exhaust gasstream 11”) provided m the range of 300-600° C. the recirculatingexhaust stream 16 is measured to be at 100-250° C. with a flow rate 3times that of the inlet exhaust stream 11. In the process, a temperatureof the resultant exhaust stream 13 gets reduced to about 120-300° C. Thedesorber outlet stream 14 in this case is having temperature of about150° C.

The proposed system and/or method of exhaust recirculation solves thedrawbacks of the conventional systems/arrangements as, in the case ofthe exhaust re-circulation as proposed herein, the temperature enteringa desorber of the sorption pump, such as a metal hydride heat pump, isnow reduced to the range of 100-250° C. as compared to 500-600° C. inconvention direct exhaust gas intake. This intake temperature is muchlower than the intake temperature of the exhaust entering the metalhydride heat pump in a conventional arrangement. This avoids overheatingof a heat transfer surface of a heat exchanger of the metal hydride heatpump.

Further, as operation of metal hydride heat pump is cyclic in nature,with alternate heating and cooling of the heat exchanger (also referredto as the ‘reactor’) in a cycle, lower temperature of the heat transfersurface results in reduced thermal inertia of the whole of the system,which not only improves the performance of the system, but also enhancescooling capacity and COP.

Further, in the present system and/or method, a temperature differenceacross an inlet and an outlet of the heat exchanger gets reducedtypically in the order of 200-100° C. Hence, volumetric flow differencebetween the inlet and the outlet is substantially lower compared to theconventional system and/or method. This results in uniform velocities ofthe exhaust gas, resulting in improved heat transfer rate.

Furthermore, in the present system and/or method, an exhaust gas flow atthe inlet of the heat exchanger is higher compared to the conventionalsystem and/or method. Owing to this, reduced number of passes or singlepass can be implemented in the heat exchanger, which in turn results inreduced pressure drop in the heat exchanger. This also results in betterdistribution of the exhaust gas over the heat transfer surface. Further,as a temperature difference across the heat exchanger is lower, chancesof thermal creep-expansion are also reduced, thus resulting in improvedreliability and a longer life of the system.

Moreover, as the heat exchanger now operates at a maximum temperature ofabout 250° C., conventional cost effective materials like carbon steels,aluminum, stainless steels, and copper can be used for the constructionof the heat exchanger.

In addition to this, the present system and/or method allows for theimplementation of a cleaning mechanism by means of a construction of aregeneration module of the reactor carrying the metal hydride sorbentmedia to clean off exhaust gas constituents such as dust, soot andexhaust gas condensates that are deposited on operative surfaces of theregeneration module.

FIG. 3 illustrates an arrangement 300 for heat recovery from exhaust gasrecirculation system 200 in a rotating type metal hydride heat pump, inaccordance with an embodiment of the present disclosure. The arrangement300 includes a first reactor assembly module 31 or A1 and a secondreactor assembly module 32 or A2, each having regeneration alloymaterial, such as high temperature metal hydride, and an fluidchangeover mechanism. Changeover of various fluid streams during a cyclechange is done by rotating the reactor assembly modules 31 and 32. Forthe purpose, a fluid stream switching means is provided in the form of arotating bearing assembly 33 having a drive mechanism, on which thereactor assembly modules 31 and 32 are mounted.

The reactor assembly modules 31 and 32 are enclosed in a housing 34along with a mixer 37. The housing 34 is provided for compartmentalizingand guiding hot air/reject exhaust gas streams 41, 38, 42, 39, 40 andambient air streams 43, 44.

One or more flexible seals 35 and non-flexible seals 36 are provided toform two compartments, each housing one reactor assembly module. Theseals 35 and 36 are provided in the corresponding air changeover systemand form compartments in stationary as well as rotating conditions ofthe reactor assembly modules 31, 32. Further, the arrangement 300consists of a flow regulating means such as a recirculation fan 45 fatsoreferred as “fan 45”) downstream of the reactor assembly modules forcompressing the cooled resultant gas stream from an outlet of thereactor assembly module 31.

The re-circulating exhaust gas has an average temperature of about80-250° C. depending on the process requirement and a recirculationrate. The recirculation rate is defined as the ratio of a re-circulatinggas stream 39 to an inlet exhaust stream 41 (also referred as “inletexhaust gas stream 41”). The recirculation rate can vary from 0.1 to 10depending on the requirement of the system. A lower circulation ratewill result in higher temperature resultant exhaust gas stream 40,whereas a higher recirculation rate will result in lower temperatureresultant exhaust gas stream 40.

A part of the compressed cooled resultant gas stream 42 (which is equalto the mass flow of the inlet exhaust stream 41 from a fan outlet) isreleased to the chimney/atmosphere. In one embodiment, an exhaust outlet49 to chimney/atmosphere can be from fan suction to atmosphere insteadof from fart outlet, i.e. the exhaust outlet 49 may be positionedupstream of the fan 45 instead of downstream. A balance re-circulatedgas stream 39 is mixed with the inlet exhaust stream 41 at hightemperature in the mixer 37. The inlet exhaust gas stream 41, which isheat source at high temperature up to 500° C. can be from an exhaust ofan engine.

The inlet exhaust gas stream 41 and the re-circulated gas stream 39 getmixed in the mixer 37 to form a uniform mixture of the resultant exhaustgas stream 40 having a temperature intermediate of the two. Theresultant exhaust gas stream 40 of the mixer 37 flows over the reactorassembly module 31. The resultant exhaust gas stream 40 has atemperature of about 300° C. and a flow rate of up to 11 times of theinlet exhaust stream 41. This exhaust gas temperature is suitable forthe efficient performance of the system. The heat of the resultantexhaust gas stream 40 gets transferred to the reactor assembly Al, wherethe metal hydride desorbs the hydrogen part of the exhaust, in theprocess, the temperature of the resultant exhaust gas gets reduced andthe cooled resultant gas stream 42 is fed to the suction of the fan 45.

In the first half of the cycle, the resultant exhaust gas flows over thereactor assembly module A1 while in the second half, the resultantexhaust gas flows over the reactor assembly module A2. A cyclechangeover from the first cycle to the second cycle and vice-a-versa isdone by the rotating bearing assembly 33 by 180° about a centralrotating axis. The rotating hearing assembly 33 uses a drive mechanismto rotate the reactor assembly modules A) and A2.

In operation, the mixer 37 mixes an inlet exhaust gas stream 41 from afirst inlet 46 and a re-circulated gas stream 39 from a second inlet 47to form the resultant exhaust gas stream 40 which exits from a resultantoutlet 48.

The reactor assembly module 31 coupled to the resultant outlet 48 actsas a desorption unit and converts the resultant exhaust gas stream 40into a cooled resultant gas stream 42. The exhaust outlet 49 is placedin the path of flow of the cooled resultant gas stream 42 such that aportion of the cooled resultant gas stream 42, hereinafter referred toas reject exhaust gas stream 38, is rejected out of the housing 34 andthe remainder of the cooled resultant gas stream 42, which is there-circulated gas stream 39 as referred to earlier, continues to travelalong its path back to the mixer 37.

The resultant exhaust gas stream 40 after passing over the reactorassembly module 31, is split into the re-circulated gas stream 39 andthe reject exhaust gas stream 38. The splitting of the cooled resultantgas stream 42 is done by providing a controlled opening/closing of theexhaust outlet 49 for the reject exhaust gas stream 38 provided in thehousing 34. The opening or closing of the exhaust outlet 49 provided issuch that a flow through it is unidirectional and any change in the flowof the inlet exhaust gas stream 41 results in a change in pressure atthe fan 45 suction and discharge. Via the exhaust outlet 49, this changein pressure matches with the reject exhaust gas stream 38 to the inletexhaust gas stream 41 pressure difference, and mass balance is thusensured.

Further, a speed of the fan 45 can be varied to control a ran dischargeflow and a recirculation rate. By varying the recirculation rate, thetemperature of the resultant exhaust gas stream 40 can be controlled, incase of a lower inlet exhaust gas temperature, the fan speed is reducedto get a lower recirculation rate. A reduced recirculation rate resultsin maintaining a constant resultant exhaust gas temperature.

Further, the exhaust outlet 49 can be placed after the fan 45, i.e., ata fan outlet; or before the fan, i.e., at a fan suction, in the firstcase, a flow handled by the fan 45 is the sum of the reject flow and there-circulated flow. This arrangement 300 allows the exhaust gasrecirculation system 200 to operate at lower pressures and thus a fansuction pressure can be slightly below the atmospheric pressure. In thisarrangement 300, the reject exhaust is blown out with the maximumpressure generated inside the system 200. In the second case, a fan flowrate is same as the recirculation flow, which results in reduced fanpower consumption. This requires operation of the exhaust gasrecirculation system 200 to be at above the atmospheric system. In thisarrangement, the reject exhaust is blown out of the system with thelowest pressure in the system 200.

FIG. 4 illustrates an arrangement 400 for heat recovery from exhaust gasrecirculation system in a damper type metal hydride heat pump, inaccordance with an embodiment of the present disclosure.

As shown, a first reactor assembly module 51 or A1 having a regenerationalloy is coupled from a hydrogen gas side to a second reactor assemblymodule 52 or B 1 having a refrigeration alloy. The two modules 51 and 52are connected to each other through a hydrogen tubing 55. Further, athird reactor assembly module 53 or A2 having a regeneration alloy iscoupled from hydrogen gas side to a fourth reactor assembly module 54 orB2 having a refrigeration alloy. These two modules 53 and 54 areconnected to each through another hydrogen tubing 56.

Further, lour electromagnetic/electro-pneumatic damper valves 57 a, 57b, 57 c, 57 d, collectively referred to as damper valves 57, each havingfour ports and two positions are used for the changeover of a heattransfer fluid/air streams over the reactor modules 51, 52, 53 and 54 inpie-determined, cyclic manner.

A flap position 61 a of the damper valves 57 provides for a firsthalf-cycle, such that the reactor modules B1 and A2 act in a desorptionmode while 132 and A1 in an absorption mode. Further, a flap position 61b of the damper valves 57 provides for a second half cycle, such that A1and B2 act in a desorption mode while B1 and A2 act in an absorptionmode.

In the first hall cycle of operation, the rector assembly A2 is in theprocess of desorption of hydrogen using a resultant exhaust gas stream(A-ir) having an intermediate temperature of about 300° C. Hydrogenreleased by the reactor assembly A2 is absorbed by the reactor assemblyB2 while the heat of absorption is released to the environment as an airstream (C-i). The resultant exhaust gas stream (A-ir) flows via a firstdamper valve 57 a and an inlet ducting 62 to the reactor assembly A2.

In the hydrogen desorption process by the reactor assembly module A2,the resultant exhaust gas stream (A-ir) gets cooled to an averagetemperature of 200° C. The cooled-down resultant exhaust gas stream(A-ir) received at an outlet of the reactor assembly A2 flows to asuction side of a re-circulating fan or blower 58 via another outletdamper valve 57 b. The recirculating fan or blower 58 is configured tohandle high temperatures up to a range of 500° C. The re-circulating,fan or blower 58 compresses the cooled-down resultant exhaust gas stream(A-ir) to a pressure higher than a mixer 59 that follows there-circulating fan or blower 58. A part of the compressed exhaust gas(A-o), which is equal to the mass flow of an inlet exhaust gas stream(A-i), from an outlet of the re-circulating fan or blower 58 is releasedto the atmosphere. In one embodiment, the exhaust gas outlet to theatmosphere can be provided from a suction side of the re-circulating (anor blower 58 instead of from the fan outlet.

Further, the remaining flow of the exhaust gas (A-r) is mixed with theinlet exhaust gas stream (A-i), which is received at a high temperatureof about 500° C., in the mixer 59. The inlet exhaust gas stream (A-i),which acts as the heat source, is provided, from example, from anexhaust of an engine. The inlet exhaust gas stream (A-i) and theremaining recirculated exhaust gas stream (A-r) get mixed in the mixer59 to form a uniform mixture of resultant exhaust gas (A-ir) having anintermediate low temperature. The recirculation rate can vary from 0.1to 10 depending on the requirement of the system.

In the hydrogen adsorption process m the reactor assembly B2, the heatof absorption is released to the atmosphere in the form of an ambientair stream (C-i), as mentioned earlier. The ambient air stream (C-i) isconnected to the reactor assembly B2 via an inlet damper valve 57 d andinlet ducting 62. In the first half cycle of operation, the rectorassembly B 1 is in the process of desorption of hydrogen using a lowtemperature source in the form of a return air stream (D-i) front thechamber 60, i.e., the enclosure to be cooled. The hydrogen released bythe reactor assembly B 1 is absorbed by the reactor assembly A1 in thefirst half cycle and the heat of absorption is released to the ambientair stream (B-i). During this process, the return air stream D-i getsfurther cooled to a temperature lower than a cold supply stream (D-o) tothe chamber 60.

During the second half cycle, the reactor assembly A1 is in process ofdesorption of hydrogen using the resultant air stream (A-ir). Thedesorbed hydrogen is absorbed by the reactor assembly B 1 and the heatof absorption is rejected to the atmosphere, through the ambient airstream (C-i). Also, the reactor assembly B2 is in the process ofhydrogen desorption using a low-temperature source in the form of returnair (D-i) from the chamber 60. The desorbed hydrogen is absorbed by thereactor assembly A2 and the heat of absorption is rejected to artambient air stream (B-i). During this process, the return air stream(D-i) gets further cooled to a temperature lower than a temperature ofthe cold supply stream (D-o) to the chamber 60.

FIG. 5 illustrates a graph showing a desorber input heat duty fromexhaust gases over time for a conventional exhaust system (referring toplots a and c) versus that of a heat pump having the system as describedherein (referring to plots b and d). As is clear from the plots, theexhaust recirculation type system has a relatively low average desorberinput heat duty from exhaust gas for a predetermined time period fordesorbing same quantity of hydrogen.

FIGS. 6A and 6B illustrate a self-cleaning arrangement 600 in a rotatingreactor type metal hydride heat pump, in accordance with an aspect ofthe present disclosure. In particular, FIG. 6A shows a reactor assemblyposition in the first half cycle of operation and FIG. 6B shows thereactor assembly position during the second half cycle in a rotatingtype metal hydride heat pump.

The self-cleaning arrangement 600 shows reactor assemblies 71 a and 71b, each containing regeneration-high temperature metal hydride. Thereactor assemblies 71 a and 71 b can be fin-tube type heat exchangerhaving a metal hydride filled inside the tubes and a heat transfermedium flowing over the fins.

The self-cleaning arrangement 600 is constructed such that it is dividedinto two thermally insulated compartments, each containing a reactorassembly, and two different heat transfer fluids flow through eachcompartment, simultaneously, in one half cycle, in a direction oppositeto that of the other. In other words, the constituents of the exhaustgas stream like dust and soot deposited on the surface of one reactorassembly, in one half cycle, are blown away in a subsequent half cycleusing ambient air stream flowing through the corresponding compartmentin an opposite direction to that of the exhaust gas stream.

The reactor assemblies 71 a and 71 b are enclosed in a thermallyinsulated housing 76 and are separated from another using a thermallyinsulated partition 72. The reactor assemblies 71 a and 71 b are mountedon a hearing assembly 75 having a drive mechanism to rotate the reactorassemblies 71 a and 71 b around an axis of rotation 73 during operation.

The housing 76 is provided to form two thermally insulated compartments,each having one reactor assembly and a different heat transfer fluid. Inan embodiment, partition flexible seals 74 are mounted on the housing 76along a diameter of each reactor assembly to avoid mixing of the heattransfer fluids from the two compartments during stationary- and/orrotating conditions. The partition flexible seals 74 are provided aboveand below the reactor assemblies 71 a and 71 b. Further, peripheralflexible seals 77 are mounted on the perimeter of housing 76 to avoidbypassing of the heat transfer fluids while flowing over the reactorassemblies 71 a and 71 b during rotating and/or stationary conditions.

Further, as shown, one heat transfer fluid 78 a is an inlet exhaust gasstream having few ppm level particulate matter/soot 80 a and 83 a. Inaddition, this inlet exhaust gas stream contains condensates of exhaustgas constituents such as acidic gas condensates, further, another heattransfer fluid 79 a is an inlet ambient air stream, which may containppm level dust particles 81 a and 82 a. Further, an exit exhaust gasstream is shown by 78 c. A direction of flow of the exhaust gas streamover the reactor assemblies 71 a and 71 b during the first and thesecond half cycles is shown by 78 b. Likewise, an exit ambient steam isshown by 79 c. A direction of flow of the ambient air stream over thereactor assemblies 71 a and 71 b during the first and the second halfcycle is shown by 79 b.

As will be easily appreciated, a soot particle quantity in the exhaustgas is normally higher compared to the ambient air. Hence, a flow rateof ambient air is always kept more titan the exhaust gas flow. Thisenables cleaning of a comparatively higher quantity of soot particlesthat is deposited on the reactor surface during one hall-cycle in onecompartment using a high flow rate of ambient air flowing inside theother compartment, in an opposite direction in comparison to the exhaustflow direction, in the next half cycle.

The soot particles settled on an entry of the reactor assembly 71 a inthe first half cycle is shown by reference numeral 80 a (referring toFIG. 6A). These particles (shown as 80 b, FIG. 6B) are pushed out by theambient air stream 79 b, which has a flow direction opposite that of theexhaust gas (low direction 78 b.

Likewise, the soot particles settled on an entry of the reactor assembly71 b in the second half cycle is shown by reference numeral 83 a. Theseparticles (shown as 83 b) are pushed out by the ambient air stream 79 b,which has a flow direction opposite that of the exhaust gas flowdirection 78 b.

Reference numeral 81 b shows dust particles pushed out by the exhaustgas flow 78 c of the reactor assembly 71 a, in relation to FIG. 6A.These dust particles (81 b) were settled on the reactor assembly duringa previous half cycle and are shown as 81 a, in relation to FIG. 6B.Here, the dust settled on reactor assemblies is pushed out by theexhaust gas stream having a direction 78 b, which is opposite to that ofthe ambient air flow, shown as 79 b.

Likewise, reference numeral 82 b shows dust particles pushed out by theexhaust gas flow out 78 c of the reactor assembly 71 b. The dustparticles (82 b) get settled on the reactor assembly during a previoushalf cycle, shown by 82 b. Here, the dust settled on reactor assembliesis pushed out by the exhaust gas stream having a direction 78 b, whichis opposite to that of the ambient air flow 79 b.

The partition flexible seals 74 provided above and below the reactorassemblies 71 a and 71 b are adapted to provide contact with a reactorassembly's surface, such that it assists in the cleaning of thedust/soot particles settled on each reactor assembly. A loose end of thepartition flexible seals 74 remains in contact with the reactorassemblies during rotation and helps loosen the soot/dust particlessettled on the reactor surface after every half-cycle. The loosenedparticles of soot/duct are carried out by the ambient air and/or theexhaust gas stream respectively, as described earlier. In a similarmanner, condensates are also cleaned off from the reactor assemblies.

FIGS. 7A and 7B illustrate a self-cleaning arrangement 700 in a dampertype metal hydride heat pump, in accordance with an aspect of thepresent disclosure.

In particular, FIG. 7A shows a reactor assembly 91 of a damper typemetal hydride heat pump with the exhaust gas stream acting as the heattransfer fluid containing ppm level soot particles in the first halfcycle, while FIG. 7B shows the reactor assembly 91 with the ambient airstream acting as the heat transfer fluid containing ppm level sootparticles in the second half cycle.

The reactor assembly 91 contains a regeneration/high temperature metalhydride alloy. The reactor assembly 91 includes a set of air valves 92 aand 92 b adapted to switch the heat transfer fluids alternatively aftereach half cycle. In relation to FIG. 7A, an inlet exhaust gas stream 93a provided to the reactor assembly 91 via the air valve 92 a flows overthe reactor assembly 91 in the first half cycle and exits as an outletexhaust stream 93 c via an air valve 92 b. The exhaust flow directionover the reactor assembly 91 is shown by 93 b. Further, in relation toFIG. 7b , an inlet ambient air stream 94 a provided to the reactorassembly 91 via the air valve 92 b flows over the reactor assembly 91 inthe second half cycle. The inlet ambient air stream 94 a exits thereactor assembly 91 as an outlet ambient air stream 94 c via the airvalve 92 a. The ambient air flow direction over the reactor assembly 91is shown by 94 b.

During the first half cycle of operation, soot particles get settled onan entry of the reactor assembly 91 (shown by 95 a). The exhaust gasstream flowing through the reactor assembly 91 carries the sootparticles out of the reactor assembly 91 (shown by 96 b), which weresettled from the ambient air stream in the previous half cycle shown by96 a. The exhaust gas stream 93 b is adapted to flow in a direction overthe reactor assembly 91 opposite to that of ambient air stream 94 b.This helps removal of the dust/soot particles out of the reactorassembly 91 via the air valve 92 b.

During the second half cycle of operation, the soot particles settled ina previous cycle 95 a at the entry of the reactor assembly are pushedout by the ambient air flow, shown by 95 b via the air valve 92 a in thesame manner as described above.

In each of the case discussed with reference to FIG. 6 (collectively)and FIG. 7 (collectively), the configuration of the other essentialfeatures of the heat recovery system will be similar to the onesdiscussed with reference to FIGS. 2 to 4. For example, the embodimentsdiscussed in the FIGS. 6 and 7 also have a recirculation circuit asdiscussed in the FIGS. 2 to 4. Further, a mixer is provided as part ofthe recirculation circuit to mix a recirculation stream with an exhaustgas stream coming from an exhaust source such as an engine. In anembodiment, the mixer is positioned within any one of the two thermallyinsulated compartments itself.

Soot particle quantity in the exhaust gas is normally higher as comparedto the dust quantity in the ambient air. Hence, a flow rate of ambientair is kept more than that of the exhaust gas flow. This enablescleaning of soot particles, which are higher in quantity, from a reactorsurface in a next half cycle by the ambient air flow having an oppositedirection when compared to the exhaust flow direction.

As can be appreciated by the a person skilled in the art, the presentrecirculation based self-cleaning arrangements are not limited to metalhydride heat pumps and can also be used for exhaust heat drivenadsorption heat pump, lithium bromide-water absorption heat pumps, andammonia water absorption heat pumps also.

Technical Advancements and Economical Significance

The technical advancements offered by the heat transfer system of thepresent disclosure include the realization of:

Improved reliability of the system.

Compact and manageable system.

Improved heat transfer rate.

Efficient self-cleaning of the reactor assemblies.

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

The use of the expression “at least” or “at least one” suggests the useof one or more elements or ingredients or quantities, as the use may bein the embodiment to achieve one or more desired objects or results.

Any discussion of documents, acts, materials, devices, articles or thelike that has been included in this specification is solely for thepurpose of providing a context for the disclosure. It is not to be takenas an admission that arty or all of these matters form part of the priorart base or were common general knowledge in the field relevant to thedisclosure as it existed anywhere before the priority date of thisapplication.

The numerical values mentioned for the various physical parameters,dimensions or quantities are only approximations and it is envisagedthat the values higher/lower than the numerical values assigned to theparameters, dimensions or quantities fall within the scope of thedisclosure, unless there is a statement in the specifications specificto the contrary.

While considerable emphasis has been placed herein on the variouscomponents of the preferred embodiment, it will be appreciated that manyalterations can be made and that many modifications can be made in thepreferred embodiment without departing front the principles of theinvention. These and other changes in the preferred embodiment as wellas other embodiments of the invention will be apparent to those skilledin the art from the disclosure herein, whereby it is to be distinctlyunderstood that the foregoing descriptive matter is to be interpretedmerely as illustrative of the invention and not as a limitation.

1. An exhaust gas heat recovery system comprising: a heat pumpconfigured to pump heat from a refrigerant, said heat pump having aninlet and an outlet wherein the exhaust gas stream leaving said outletis split into two streams: a stream rejected to atmosphere and arecirculating exhaust stream re-circulated back to said heat pump; amixer provided at said inlet of said heat pump to mix an inlet exhauststream with said recirculating exhaust gas stream to get a resultantexhaust stream at an intermediate temperature of the two streams; and aflow regulating means adapted to compress said recirculating exhauststream.
 2. The exhaust gas heat recovery system as claimed in claim 1,wherein said heat pump is a sorption heat pump having a desorber fordesorbing a refrigerant material by taking heat from a heat source. 3.The exhaust gas heat recovery system as claimed in claim 1, wherein saidresultant exhaust stream has the same heat content as that of said inletexhaust stream but an increased flow rate and a lower temperature ascompared to said inlet exhaust stream.
 4. The exhaust gas heat recoverysystem as claimed in claim 2, wherein direction of flow of ambient airis opposite to the direction of flow of exhaust gases through said heatpump.